1. Field
This disclosure relates generally to amplifiers, and more specifically, to a digital pulse width modulated feedback system for a switching amplifier and method therefor.
2. Related Art
Digital audio switching power amplifiers are well known and widely used. Most digital audio switching power amplifiers are based on pulse width modulation (PWM). A PWM signal is presented to a switching amplifier that performs a level shifting function to translate the PWM signal to a digital PWM signal having significantly higher voltage levels. The audio fidelity of the switching power amplifier is influenced by nonidealities of the system. In the system, feedback from a switching power stage is used to provide a correction signal to remove, for example, power supply noise. However, the feedback may not correct for problems caused by components following the switching power stage, such as for example, a low pass filter (LPF) coupled between the switching power stage and a speaker load. A LPF may have a variable frequency response and nonlinearity. Also, there may be an interaction between the variable frequency response of the LPF and a variable speaker load impedance that adversely affects signal quality. Therefore, it would be desirable to have feedback from the LPF rather than from the power stage. However, there is a significant amount of delay in the LPF which makes providing agile feedback from the LPF difficult.
Therefore, what is needed is a feedback system that solves the above problems.